ZnO thin films have been elaborated by Pulsed Laser Deposition (PLD) onto glass substrates, at room temperature. Post-growth annealing treatment was applied to the films in air background. Morphology, chemical composition and optical characteristics of ZnO films were evaluated as a function of annealing temperature. With the increase in annealing temperature, the 002 axis peak intensity is improved and optical band gap is shifted to lower values. The PL peak positions shift are associated at stoichiometry change, it is confirmed with the experimental results. The films elaborated with this experimental setup could be used to applications in short wavelength optoelectronic devices, chemical and optical sensors.